Triangulation and Levelling

The triangulation method was adopted to provide the geometrical basis and framework of the map. This meant superimposing a network of triangles over the territory. Based on an exact measurement of distance in Grossen Moos and above all by measuring the angles of all the points of the triangles, the so-called triangulation points, their coordinates could be calculated. In this way the first accurate geometric reference network for the whole country came into being, one that made the link between the regions to the North and to the South of the Alps.

In order to fix the height of the mountains not only in relation to each other, a point was needed, a so-called height horizon, the precise height of which above sea-level needs to be known. But Switzerland has no borders with the sea, so how can the height above sea level be measured? The reference point for determining the level of the land is the Pierre du Niton, the larger of the two boulders in the harbour of Geneva. It was selected in 1820 by Dufour himself and serves as the reference point for all height measurements in Switzerland. Its height was originally determined via corroboration with French reference points, but later on accurate measurements were carried out vs. the tide gauges installed in neighbouring countries.